This application is based on application Nos. 11-348489 and 2000-176673 filed in Japan, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a light shutter device, and more particularly to a light shutter device which has a plurality of light shutter elements on a substrate with an electro-optical effect and which turns on and off the light by applying a voltage to the light shutter elements.
2. Description of Related Art
Conventionally, various kinds of light shutter devices have been developed to be used to form an image on silver salt photographic paper or film, or an electrophotographic photosensitive member. Such a light shutter device has light shutter chips made of PLZT, which is a material with an electro-optical effect, arranged in an array and controls turning on/off of the light pixel by pixel.
More specifically, as FIG. 17 shows, when a voltage is applied between a pair of electrodes 32 and 33 provided on a light shutter chip 30, the PLZT of the chip 30 causes birefringence. In this state, light which is incident to a light transmitting portion (light shutter element) 31 via a polarizer 35 which is arranged before the light shutter chip 30, is polarized by 90 degrees, and light is emergent from the light transmitting portion 31 and passes through an analyzer 36. Thus, light is turned on.
When the light transmitting portion polarizes the incident light at 90 degrees, the portion can transmit the light at the maximum, and the voltage applied between the electrodes to achieve the maximum quantity of transmitted light is referred to as a half-wave voltage. Therefore, light shutter elements of this kind are driven with the half-wave voltage applied; however, because of crosstalk between adjacent light shutter elements, the quantity of transmitted light fluctuates.
As far as one light shutter element is concerned, when all the light shutter elements of the device including the element concerned are turned on (all lighting), the light shutter element has a light transmitting characteristic shown by the curve A in FIG. 4a. On the other hand, when only the light shutter element concerned is turned on (single lighting), the light shutter element has a light transmitting characteristic shown by the curve B in FIG. 4a. In the case of FIG. 4a, when the half-wave voltage at the time of entire lighting is applied to the light shutter element for single lighting, the quantity of transmitted light is reduced approximately 12%, compared with the quantity of transmitted light when the same voltage is applied for all lighting. There is an approximately 25V shift in half-wave voltage between the time of all lighting and the time of single lighting.
In order to solve the problem, Japanese Patent Laid Open Publication No. 60-159722 suggested that shield electrodes are provided to extend from a common electrode to among light shutter elements. Also, Japanese Patent Laid Open Publication Nos. 58-95320 and 58-130321 suggested that grooves are provided among individual electrodes to prevent crosstalk.
However, the former measure has the following demerits: this is not suited to produce high-definition devices because the shield electrodes and the individual electrodes are too close to one another; and stray capacity occurring among the individual electrodes and the shield electrodes are large, which results in an increase in power consumption. Also, the latter measure has a demerit that this is not suited to produce high-definition devices because forming grooves among the individual electrodes complicates the manufacturing process.
An object of the present invention is to provide a light shutter device in which crosstalk between adjacent light shutter elements can be suppressed and which is easy to be produced and easy to be made into a high-definition device.
Another object of the present invention is to provide a light shutter device which has a low half-wave voltage.
In order to attain the objects, a first light shutter device according to the present invention comprises: a planar substrate with an electro-optical effect; and a plurality of pairs of electrodes provided on the substrate, portions of the substrate between the respective pairs of electrodes functioning as light shutter elements when electric fields act between the respective pairs of electrodes; wherein, suppose the electrodes in each pair are at a distance L from each other and a side which extends in a direction perpendicular to the direction of electric field of one of the electrodes in each pair has a dimension W, W/L greater than 2.
The present inventors gave an attention to the relationship between the distance L between the electrodes in each pair and the dimension W of one of the electrodes in each pair. In conventional devices, W/L is around 1. As a result of experiments, however, when W/L greater than 2, crosstalk between adjacent light shutter elements could be suppressed, and there was substantially no difference in quantity of transmitted light between a time of all lighting and a time of single lighting. This first light shutter device according to the present invention requires neither shield electrodes nor grooves among the light shutter elements, and accordingly, this device can be fabricated easily and can be made into a high-definition device easily. Moreover, this invention is not accompanied with an increase in power consumption, while providing shield electrodes results in an increase in power consumption.
In the first light shutter device, further, suppose one of the electrodes in each pair has a dimension D in the direction of electric field, preferably D/L greater than 0.5. On this condition, the half-wave voltage is lower.
A second light shutter device according to the present invention comprises: a planar substrate with an electro-optical effect; a common electrode which extends in a specified direction on the substrate; and a plurality of individual electrodes which are arranged along the common electrode so that each of the individual electrodes faces the common electrode, portions of the substrate between the common electrode and the respective individual electrodes functioning as light shutter elements when electric fields act between the common electrode and the respective individual electrodes; wherein suppose each of the individual electrodes faces the common electrode at a distance L, each of the light shutter elements is at a distance not less than 5L from each of the individual electrodes which drive the other light shutter elements.
The present inventors gave an attention to the positional relationship between each of the light shutter elements and the individual electrodes which drive the other light shutter elements and conducted various experiments about the relationship between the distance L between each of the individual electrodes and the common electrode, which means the dimension of each light shutter element in the direction of electric field, and the distance between the light shutter element and each of the individual electrodes which drive the other light shutter elements. As a result, when a light shutter element was located at not less than 5L from each of the individual electrodes which drive the other light shutter elements, crosstalk between the light shutter element and the adjacent elements could be suppressed, and the shift in half-wave voltage and the reduction in quantity of transmitted light at the time of single lighting were in an extent to cause substantially no problem.
A third light shutter device according to the present invention comprises: a planar substrate with an electro-optical effect; a common electrode which extends in a specified direction on the substrate; and a plurality of individual electrodes which are arranged along both sides of the common electrode so that each of the individual electrodes faces the common electrode, portions of the substrate between the common electrode and the respective individual electrodes functioning as light shutter elements when electric fields act between the common electrode and the respective individual electrodes; wherein the common electrode is separated by a groove which extends in the specified direction.
Since the common electrode is separated by a groove, crosstalk between the light shutter elements which are located on both sides of the common electrode can be suppressed, and the quantity of transmitted light at a time of single lighting is almost equal to that at a time of all lighting. Forming one groove is enough, and this does not complicate the manufacturing process of this light shutter device.
Further, in the third light shutter device, suppose each of the individual electrodes faces the common electrode at a distance L, each of the light shutter elements is preferably at a distance not less than 5L from each of the individual electrodes which drive the other light shutter elements. With this arrangement, crosstalk between adjacent light shutter elements can be suppressed more.